#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main() {
	int n = 0;
	scanf("%d", &n);
	int temp = 0;
	int nums = 0;
	for (int i = 0; i < n; i++) {
		scanf("%d", &nums);
		temp ^= nums;
	}
	printf("%d", temp);
	return 0;
}